PURPOSE: To reduce storage area and to process a circuit diagram of a large scale by processing a connecting relation closed in a drawing, the connecting relation covering the drawings, and the connecting relation covering the hierarchies while reading successively the drawings and deleting a processed store structure after its processing.

CONSTITUTION: A logic circuit diagram data base 2 stores the data on a store structure showing the connecting relation between the elements into a logic circuit diagram which is divided for each hierarchy consisting of one or more sheets of drawings. A connection rule data base 3 stores a connection rule showing the propriety of the connecting relation. Then a circuit diagram connection inspecting part 1 reads successively the divided drawings and at the same time processes the connecting relation between the elements closed in a single drawing or hierarchy for each hierarchy. The connecting relation between the elements is extracted and inspected by a system itself based on the connection information in regard of the connecting relation covering the hierarchies. Then the processed store structure is deleted after processing. Thus it is possible to reduce the working capacity of a main storage storing the store structure and to process a circuit diagram of a large scale.